I recently made a poor-man's ice cream by making an egg custard and freezing it in the freezer in a metal bowl, stiring about every half hour. I was expecting it to freeze it 2 hours, but three hours later, it was too late, still not frozen solid and I went to bed.

The resulting ice cream was edible, but had more crystals than one might want.

What other techniques are there for freezing the ice cream short of buying an ice cream machine? Or can this recipe be improved?

My cub scouts love to make camp out ice cream. You will need two cans, one significantly larger than the other both with lids (we use a #10 coffee can and a small coffee can). Make sure the small, inner can is clean and fill 2/3 of the way with an ice cream or custard mix (it will expand with churning as air is added). Place small can inside of larger can and surround with ice and a sprinkle of rock salt (or kosher salt). Roll cans back and forth for 30 minutes or so to get to soft serve consistency (more ice may need to be added half way through) you can place small can in freezer after it has reached soft serve for more solid consistency without the crystals.

Similar to the technique Janelle outlines you can do the same thing with zip-loc bags.

Fill a smaller one with the ice cream mixture and a larger one with ice and rock salt. Put the smaller inside the larger and then 'massage' the bags until ice cream is made. you can do this with your feet whilst you watch TV.

If you can get hold of enough dry ice to surround a metal mixing bowl, it should be possible to make ice cream by whipping whole milk in the bowl. This wouldn't work with dry ice blocks. With chips or shavings it ought to.